This application is a 371 of PCT/EP00/11866 filed Nov. 28, 2000.
The invention concerns a rotary piston adjuster for adjusting the angular position of the camshaft of an internal combustion engine said adjuster comprising an outer rotor connected to a drive pinion and an inner rotor connected to the camshaft, the outer rotor comprising at least one hydraulic chamber having radial separating walls and the inner rotor comprising at least one pivoting vane that sealingly divides the hydraulic chamber into working chambers A and B and can pivot hydraulically between a retard stop position and an advance stop position, said adjuster further comprising a locking device suitable for detachably connecting the outer and the inner rotors.
During the stopping and starting phases of an internal combustion engine, clattering noises are caused by the alternating torque of the camshaft when the rotary piston adjuster has been drained. To prevent these noises, the outer rotor and the inner rotor of the rotary piston adjuster are connected to each other in the start position which, in the case of a rotary piston adjuster of an inlet camshaft is the retard position and in the case of a rotary piston adjuster of an outlet camshaft, the advance position. In this way, besides a suppression of noise, a reliable engine start is also obtained.
There are numerous solutions for a reciprocal locking or latching of the outer and the inner rotor. The generic document DE 197 26 300 A1 discloses a rotary piston adjuster that is configured as a vane-type adjuster for adjusting the angular position of the camshaft of an internal combustion engine, said adjuster comprising an outer rotor connected to a drive pinion and an inner rotor connected to the camshaft. The outer rotor comprises at least one hydraulic chamber with radial separating walls, and the inner rotor comprises at least one pivoting vane that sealingly divides the hydraulic chamber into a working chamber A and a working chamber B while being hydraulically pivotable between a retard and an advance stop position. Further, a locking device for detachably connecting the inner and outer rotors is also provided.
This vane-type adjuster comprises in one of the vanes, an axially arranged, spring-loaded fixing pin whose conical tip is adapted to be introduced into a matching conical aperture in an end cover of the vane-type adjuster in one of the stop positions. Due to the slightly eccentric movement of the conical tip of the fixing pin into the conical opening, the pin has a wedge effect that results in a clearance-free locking of the outer and inner rotors. This latching and locking device operates reliably but is complex and prone to wear.
The object of the invention is therefore to provide a reliably operating, inexpensive and durable locking device for a rotary piston adjuster of the pre-cited type.
The division of the rotary piston adjuster into the adjuster, as such, and the attachment comprising the locking device and the stops permits the use of an optimum material for the intended purpose in each case. Thus, for example, the not so highly loaded outer and inner rotors can be made of soft materials, like light metals or plastic, and the pointwise highly loaded components of the locking device and the stops can be made of wear-resistant materials such as hardened steel. The easy-to-work soft materials reduce the cost of construction and the wear-resistant materials reduce the space requirement, while the durability and the operational reliability of the rotary piston adjuster are enhanced.
A further advantage of the inventive solution is that the same type of attachment can be used with different types of rotary piston adjusters, and its modification is possible independently of the rotary piston adjuster.
The fact that the attachment at the same time forms the end closure of the outer rotor leads to a saving of axial design space. However, it is also conceivable to configure the drive pinion as an intermediate plate and arrange the locking device and the stops on the drive end while closing the end of the rotary piston adjuster directed away from the camshaft with a simple cover.
Advantageously, the locking device comprises a locking body configured as a flat slide that is guided in a guide groove of the intermediate plate that is connected to the outer rotor. Such a locking body requires only a small axial design space and is simple to make.
According to another advantageous feature of the invention, the disc-shaped bushing that is connected to the inner rotor is sealingly guided in a coaxial bore of the intermediate plate as well as between the side washer and the cover, and the intermediate plate comprises on the periphery of its coaxial bore, a circular segment-shaped recess into which the guide groove opens and whose radially extending end surfaces are configured respectively as a retard and an advance stop. Since the intermediate plate is made of a wear-resistant material, its stops and the guide groove are also wear-resistant.
According to still another advantageous feature of the invention, a peg is arranged on the outer periphery of the disc-shaped bushing and comprises a first and a second radially extending side surface serving as stop surfaces, said peg being pivotable in the circular segment-shaped recess of the intermediate plate between its retard and advance stops. Since the disc-shaped bushing is made of a wear resistant material, the stop surfaces of the peg are also wear-resistant.
The important thing is that, depending on the position of the guide groove in one of the two stop positions of the peg, the locking body can be pushed by a locking spring into the circular segment-shaped recess at an acute angle xcex1 to one of the radially extending side surfaces of the peg till a pressure contact acting in peripheral direction is established between a preferably radially extending pressure contact surface of the locking body and one of the radially extending side surfaces of the peg. With an appropriate position of the radial guide groove, it is possible to lock the inner rotor on the advance stop (outlet camshaft) or on the retard stop (inlet camshaft). That radially extending side surface of the peg that is not in abutment with the stop serves in each case as a counter surface of the locking body when it is in the locking position. The locking body is pushed by the locking spring toward the center till the rotational lash becomes equal to zero. The adjustment of the rotational lash required during the assembly of the rotary piston adjuster for reducing noise can thus be dispensed with in the locking device of the invention. The device is even self-locking i.e., an enlargement of the rotational lash due to wear is compensated for by an inward displacement of the locking body by the locking spring.
Due to the fact that the locking body, by reason of the magnitude of the angle xcex1 included between its pressure contact surface and its direction of displacement is situated at the borderline of self-locking (quasi self-locking), an unlocking of the locking body under the influence of torque as well as a non-releasable clamping are prevented. This means that the rotary piston adjuster has a high operational reliability.
In an advantageous embodiment of the invention, the spring-distal end of the locking body is in fluid communication with the working chamber A, and its spring-proximate end is preferably in fluid communication with the working chamber B. In the case of an inlet camshaft that is generally locked in the retard position, the rotary piston adjuster bears, at least temporarily, against the retard stop under the influence of the frictional torque of the camshaft when the engine is started. The oil pressure required in the working chamber A for overcoming the frictional torque is then also sufficient for a clamp-free unlocking of the locking body.
Conditions are different in the case of an outlet camshaft whose rotary piston adjuster is generally locked in the advance position. When the internal combustion engine is started, the frictional torque of the camshaft, that acts in the same direction as the oil pressure of the working chamber A, causes the rotary piston adjuster to lift from the advance stop which results in a clamping of the locking body. For this reason, the locking body has first to be relieved of load by a pressurizing of the working chamber B to be subsequently unlocked without clamping by this very oil pressure. To maintain the unlocked state even when the working chamber A is pressurized, the locking body must also be pressurizable with the oil pressure of this working chamber. This can be realized with a stepped locking body whose end face is acted upon by the oil pressure of the working chamber A and whose stepped shoulder is acted upon by the oil pressure of the working chamber B.
The locking spring of the locking body can be configured as a coil compression spring (a single spring or a plurality of springs) or as a mini block spring. It can be made of a circular spring wire or, with the aim of enhancing the design-space-related energy absorption, of a rectangular spring wire. The mini block spring can have a slightly conical configuration. In this way, when the spring is compressed, the turns can get inter-inserted so that a small overall height is obtained.
It is of advantage if the separating walls and the pivoting vanes are spaced from each other in the direction of pivot even in the stop positions. This is made possible by the external stops that render an abutment between the separating walls and the pivoting vanes superfluous. The space formed by the spaced arrangement in the direction of pivot serves for the collection of chips and dirt particles out of the oil circuit. The shape of this space is defined in the present case by the radially extending side surfaces of the separating walls and the parallel side walls of the pivoting vanes.
In an alternative embodiment of the locking device, the locking body is configured as a flat slide that is guided in a radial guide groove in the end face of one of the separating walls of the outer rotor and can be displaced into an opening of the inner rotor in one of the stop positions of the inner rotor. Due to the fact that the radial guide groove of the locking body is disposed in the end face of one of the separating walls and the opening is disposed in the end face of the inner rotor, this locking device does not require any additional design width. This also applies to the stops if these are arranged in the interior of the rotary piston adjuster.
Advantageously, the opening is configured in the end of the inner rotor as a groove extending parallel to the axis of the inner rotor on the periphery thereof. One of the legs of the groove comprises a radially extending bevel that can be brought into a pressure contact in peripheral direction with a corresponding counter bevel of a pressure contact surface of the locking body through an inward displacement of the locking body by the spring force of a locking spring. This arrangement of the locking body offers the same advantages relative to the compensation of lash caused by assembling and wear conditions and relative to the self-locking of the locking body as the embodiment comprising an attachment. In the present embodiment, too, the stops can be arranged in an attachment.
Advantageously, the groove is in fluid communication with the working chamber Axe2x80x2 through a radial groove arranged in the end of the inner rotor, and the spring-proximate end of the locking body is in fluid communication preferably with the working chamber Bxe2x80x2 through a vent groove arranged in the end face of a separating wall. As for a clamp-free unlocking in the advance or retard position, the same applies as in the embodiment comprising an attachment. The magnitude of the unlocking force can be influenced through the width of the locking body. It is also conceivable to configure the locking body as a flat slide whose guide surfaces form a wedge shape with each other. However, a drawback of this is the inadequate lateral guidance outside of the end position.
Other locking devices are also conceivable, for example, in the form of a slightly conical locking pin which emerges axially or radially out of the outer rotor to be positioned in front of a pivoting vane that is in a stop position. A drawback of this is the axial and radial space requirement of the locking pin in the unlocked state. For a clamp-free unlocking in both stop positions, the pin must have a stepped configuration comprising functional surfaces and connecting ducts for the pressure oil of both chambers.
Other camshaft adjusters known from the prior art can be locked in any desired position. A locking of the inner rotor in different positions between the stop positions can be achieved with the inventive solution by using a plurality of locking bodies. Alternatively, the locking body may be configured so as to additionally engage into a recess on the periphery of the peg of the disc-shaped bushing.